Reduce heartbeat message

[NingLin-P]

With current implement, a MsgHeartbeat do these things:

• update( or correct ) a peer's status like commit index, StateRole, ect.
• confirm quorum for quorum check or read index request

While the MsgAppend already do the first, and the second are also easy to done
by attach the ctx with MsgAppend, we can reduce MsgHeartbeat by :

1. when sending a MsgAppend check if the heartbeat_elapsed reach a threshold
2. if it does reset the heartbeat_elapsed and attach the ctx on this msg if there is one

is it possible to implement and improve a bit performance ?

[Fullstop000]

Do you mean reducing the size of MsgHeartbeat or just canceling heartbeats?

[NingLin-P]

Canceling heartbeats.

[Fullstop000]

How does a follower keep not becoming a candidate without receiving heartbeats? OTOH, what if the current leader steps down?

[NingLin-P]

1. when follower received messages from leader, it reset election_elapsed:

            MessageType::MsgAppend => {
                self.election_elapsed = 0;
                self.leader_id = m.from;
                self.handle_append_entries(&m);
            }
            MessageType::MsgHeartbeat => {
                self.election_elapsed = 0;
                self.leader_id = m.from;
                self.handle_heartbeat(m);
            }
            MessageType::MsgSnapshot => {
                self.election_elapsed = 0;
                self.leader_id = m.from;
                self.handle_snapshot(m);
            }

2. if the current leader steps down, it will be handle as before.

BTW canceling heartbeats do not mean cancel all heartbeats, just reset the heartbeat_elapsed
and delay or avoid a heartbeat.

[BusyJay]

Do you mean not to send a heartbeat if an append message is sent within an heartbeat_elapsed ticks?

I think it can bring little improvement. When under high load, heartbeat message count is way too smaller than the count of message append; when group is idle, there is too few append messages that heartbeat message is always sent out. There should still be an improvement depends on the configuration of heartbeat-elapsed though.

[Fullstop000]

Ok, I think I've gotten the idea you described: only sending heartbeats when there are no MsgAppend msgs sent in a heartbeat_timeout.

It sounds like a good idea :).

[NingLin-P]

Yes, what you guy said is right.

[Fullstop000]

As for implementation should be quite simple I think, you can try to just set the leader's heartbeat_elasped to 0 when sending MsgAppend (or MsgSnapshot) @NingLin-P

[NingLin-P]

OK, let me try.